The present invention relates to an improved edge seal assembly for use with applicators of the trailing blade type for applying a coating liquid to a moving web of paper.
Conventional applicators of the trailing blade type include means for applying coating material to a paper web that is usually supported and carried by a resilient backing roll. Such applicators may include a chamber having an opening extending across and parallel to the web, together with a doctor blade located on the trailing side of the opening, which serves to level the coating, and a front wall extending from a leading side of the opening toward the web. Means are provided for supplying coating liquid to the chamber, and thence through the chamber opening and into an application zone defined between the front wall and doctor blade for application onto the web. To seal the end spaces between the front wall and doctor blade to prevent escape of coating material laterally of the web and out of the side ends of the application zone, edge dam means are provided thereat.
For applicators of the foregoing types, the edge dam means may comprise a flexible element at each end space for sealing with the front wall, doctor blade and paper web. Ideally, the edge dam absolutely prevents passage of any coating liquid to exterior of the application zone, thereby to maintain an uncoated margin along the side edge of the web and to prevent contamination of the web side edge, for example by eliminating excess coating material, which causes edge stickers when the web is wound on a reel.
However, in practice it is very difficult to prevent leakage of coating material past the edge dam, particularly with applicators of the type disclosed in Damrau et al U.S. Pat. No. 4,250,211, assigned to the assignee of the present invention. In that applicator, the opening from the chamber extends transversely across the application zone, and coating liquid under pressure in the chamber is introduced through the opening into the zone in copious excess to substantially completely and continuously fill the zone and a gap defined between the web and an upper edge of the front wall to form a liquid seal in the gap and thereby maintain the coating liquid in the zone under pressure for pressurized application onto the web. Because the coating liquid in the application zone is under pressure, and since the opening extends transversely across the zone so that coating liquid flowing through the side ends of the opening is directed against the edge dams, there is a direct pressure of coating liquid on the edge dams and an increased tendency for coating liquid to seep therepast.